How to install PHP 5.6 and 7.0 – 8.4 with PHP-FPM and FastCGI mode for ISPConfig 3.2 with apt on Ubuntu 22.04 – 24.04
When using ISPConfig, by default, you only have the main PHP version for your distribution. This guide will show you how to install additional PHP versions (5.6, 7.0 - 7.4, 8.1 - 8.4) on an Ubuntu server with ISPConfig.
Source: Howtoforge Linux Howtos und Tutorials